# Using a Primordial Gravitational Wave Background to Illuminate New Physics

## TL;DR

A primordial gravitational wave background can reveal new physics at high energies by imprinting signatures related to particle content changes in the early universe, detectable by future space-based detectors.

## Contribution

This work demonstrates the potential of gravitational wave observations to probe particle physics phenomena at energies around 100 TeV, complementing collider experiments.

## Key findings

- Detectable gravitational wave signatures of early-universe particle physics changes.
- Sensitivity of space-based detectors like LISA to physics near 100 TeV.
- Potential to address beyond Standard Model issues such as dark matter and baryogenesis.

## Abstract

A primordial spectrum of gravitational waves serves as a backlight to the relativistic degrees of freedom of the cosmological fluid. Any change in the particle physics content, due to a change of phase or freeze-out of a species, will leave a characteristic imprint on an otherwise featureless primordial spectrum of gravitational waves and indicate its early-Universe provenance. We show that a gravitational wave detector such as the Laser Interferometer Space Antenna would be sensitive to physics near 100 TeV in the presence of a sufficiently strong primordial spectrum. Such a detection could complement searches at newly proposed 100 km circumference accelerators such as the Future Circular Collider at CERN and the Super Proton-Proton Collider in China, thereby providing insight into a host of beyond Standard Model issues, including the hierarchy problem, dark matter, and baryogenesis.